Management of spent high activity radioactive sources

76 Pages·2002·1.23 MB·English

IAEA-TECDOC-1301
Management of spent high
activity radioactive sources
(SHARS)
September 2002
The originating Section of this publication in the IAEA was:
Waste Technology Section
International Atomic Energy Agency
Wagramer Strasse 5
P.O. Box 100
A-1400 Vienna, Austria
MANAGEMENT OF SPENT HIGH ACTIVITY RADIOACTIVE SOURCES (SHARS)
IAEA, VIENNA, 2002
IAEA-TECDOC-1301
ISBN 92–0–114502–0
ISSN 1011–4289
© IAEA, 2002
Printed by the IAEA in Austria
September 2002
FOREWORD
Sealed Radioactive Sources have found diverse applications in many agricultural, industrial
and medical uses as well as other technical and scientific research areas. Some of these areas
and applications require that the radioactivity involved be high. In earlier applications, a
relatively long lived radioisotope (Cs-137, half-life ~30 years) was utilized. Over time, source
manufacturers have tended to use shorter lived radioisotopes (Co-60, ~5-year half-life),
however many such sources had already been manufactured using longer lived isotopes. Many
early sources, not manufactured to current standards, were utilized when no clear regulatory
control was enforced and with no clear vision of their destiny once declared as waste.
Moreover, they are sometimes stored under unacceptable conditions or have escaped
regulatory control.
Most of these sources have high specific activity and therefore are relatively small in size,
increasing the probability of their loss and misplacement. The risk of their involvement in an
accident is relatively high if proper management is not adopted. Such accidents can be over
exposures to individuals or contamination of the environment. The physical characteristics of
the sources make them easily transported through borders, giving the potential of causing
harm not only in their country of origin but also beyond.
Accidents involving loss of control of high activity sources have occurred every year, causing
deaths of several people and varying injuries to a larger number of persons somewhere in the
world. This has increased the awareness of the problem and many countries are in the process
of setting up infrastructures to manage such sources safely. On the international level, the
IAEA has developed an action plan (GOV/1999/46-GC(43)) aiming at enhancing the IAEA’s
programme on the subject and initiating new activities. One of these activities is the
development of this report to specifically provide information on the management of high
activity sealed radioactive sources.
This publication provides technical advice to those who need to manage disused and spent
high activity sources and discusses relevant issues involved. It also provides background
information for any possible technical assistance to be provided and serves as a reference for
technical staff sent by the IAEA to provide advice to Member States.
Because of the current problems involved — namely that a large number of these sources have
no licensed transport container and no valid special form certificate — rendering them safe is
a difficult task. International co-operation on this subject may be required to rectify the
situation. The report can also serve as a basis to establish future co-operation.
The IAEA officer responsible for the publication was M. Al-Mughrabi of the Division of
Nuclear Fuel Cycle and Waste Technology.
EDITORIAL NOTE
The use of particular designations of countries or territories does not imply any judgement by the
publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and
institutions or of the delimitation of their boundaries.
The mention of names of specific companies or products (whether or not indicated as registered) does
not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement
or recommendation on the part of the IAEA.
CONTENTS
1. INTRODUCTION..................................................................................................................1
1.1. Background.....................................................................................................................1
1.2. Objective.........................................................................................................................1
1.3. Scope..............................................................................................................................2
1.4. Structure..........................................................................................................................3
1.5. Definitions......................................................................................................................3
2. CURRENT STATUS OF SPENT HIGH ACTIVITY RADIOACTIVE
SOURCES.............................................................................................................................4
2.1. Manufacture of sources...................................................................................................4
2.2. World inventory..............................................................................................................4
2.3. Examples of equipment containing high activity radioactive sources............................4
2.3.1. Industrial irradiators.............................................................................................4
2.3.2. Teletherapy equipment.........................................................................................5
2.3.3. Research irradiators..............................................................................................7
2.3.4. Industrial radiography equipment.......................................................................11
2.3.5. Brachytherapy equipment...................................................................................13
2.3.6. Nuclear logging equipment................................................................................14
2.3.7. Industrial gauges.................................................................................................16
3. GENERAL MANAGEMENT ISSUES...............................................................................17
3.1. Limiting the number of shars within the territory.........................................................17
3.2. Recycling or re-use.......................................................................................................17
3.3. Handling unexpected SHARS......................................................................................18
3.4. Storage prior to disposal...............................................................................................18
3.4.1. Decay storage......................................................................................................18
3.4.2. Interim storage....................................................................................................19
4. TECHNICAL ASPECTS OF MANAGEMENT OF SPENT HIGH
ACTIVITY SEALED SOURCES.......................................................................................20
4.1. Introduction..................................................................................................................20
4.1.1. Technical implementation..................................................................................21
4.2. Temporary storage........................................................................................................22
4.2.1. Preparation for temporary storage......................................................................23
4.2.2. Temporary storage facility..................................................................................24
4.2.3. Administrative controls and documentation.......................................................24
4.2.4. Examples............................................................................................................25
4.3. Transport of high activity radioactive sources..............................................................26
4.3.1. Source transported in original source holder......................................................28
4.3.2. Source removed from the original equipement..................................................31
4.4. Interim storage..............................................................................................................36
4.4.1. Preparation for interim storage...........................................................................36
4.4.2. Interim storage facilities.....................................................................................39
4.4.3. Administrative controls and document retention...............................................41
4.5. Disposal........................................................................................................................41
4.5.1. Characteristics of high activity spent sources relevant to disposal.....................42
5. LEGAL, REGULATORY AND ECONOMIC CONSIDERATIONS.................................43
5.1. General legal considerations for management of radioactive material.........................43
5.1.1. Typical legal obligations.....................................................................................43
5.1.2. Financial considerations: costs for transfer of radioactive
material and meeting legal requirements...........................................................45
5.1.3. Other financial considerations............................................................................46
5.2. Legal and financial problems contributing to radiological accidents...........................47
5.2.1. Inadequate financing of the ownership transfer costs.........................................47
5.2.2. Facility bankruptcy or other unplanned closure.................................................47
5.2.3. Unavailability of an ownership transfer path......................................................47
5.2.4. Inadequate regulatory oversight..........................................................................47
6. SUMMARY AND CONCLUDING REMARKS................................................................48
APPENDIX..............................................................................................................................51
REFERENCES.........................................................................................................................69
CONTRIBUTORS TO DRAFTING AND REVIEW..............................................................70
1. INTRODUCTION
1.1. BACKGROUND
The applications of sealed radioactive sources have been widespread. The nature and quantity
of the radionuclides utilised depend on the intended purpose. While most sources are of
relatively low activity, there are many of high or very high activity. These high activity
sources have been responsible for most of the radiological accidents involving loss of life or
disabling injuries to the public [1].
High activity sources are utilised for various applications: for example, sources of the order of
100 TBq (several thousand curies) are used worldwide for teletherapy in radiology. Sources in
the TBq–PBq range (up to tens of thousands curies) are used in research irradiators and
sources of tens of PBq (several hundred thousand curies) are used for sterilisation and food
irradiation.
The radionuclides which have been most commonly used to produce high activity sources are
Co-60, Cs-137 and Ir-192. There are also a small number of applications which use other
radionuclides such as Sr-90 and Am-241 mixed with beryllium to produce neutron sources.
The IAEA-TECDOC-1191, “Categorization of Radiation Sources” [2], lists the various
applications for each of the radionuclides of interest, along with the likely range of activity for
that application.
There are large number of high activity sealed radioactive sources in use world wide. Due to
the limited operational lifetime of sealed radioactive sources there are many that are no longer
in use and require safe management.
Many reports discuss the management of radioactive waste generated by nuclear power plants.
There are also some reports on the management of spent sealed radioactive sources. However,
there are no reports known that have been prepared specifically to address the management of
spent high activity radioactive sources (SHARS). This publication describes the management
options that are currently available for SHARS and also discusses the development of a waste
management strategy within the context of international experience.
1.2. OBJECTIVE
The objective of this report is to provide all people involved in the handling and management
of high activity sources with sufficient information about processes that are required for the
safe management of SHARS. This includes examples of spent source management that are
already taking place and also a description of the range of appropriate options that are
available for each stage in the management process. This report also aims to identify the
important issues to be addressed in order to develop a waste management strategy as part of
the integrated management strategy that takes account of international experience and the
guidance and principles that have been learned from that experience.
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1.3. SCOPE
This report relates specifically to SHARS, which are spent sources that have the potential,
with short exposures, to produce acute health effects if handled incorrectly. In addition, they
may also incur significant economic costs in any retrieval or environmental remediation
operation, following loss of or damage to such a source. SHARS therefore include all of the
sources in Category 1 of the document “Categorization of Radiation Sources” [2], i.e.
industrial radiography, teletherapy equipment and irradiators. Many sources in Category 2 also
have such potential, for instance, high activity sources used in brachytherapy, fixed industrial
gauges and well logging. Table I, while not exhaustive, lists typical sources which fall within
the scope.
TABLE I. ACTIVITY RANGE FOR VARIOUS RADIONUCLIDE APPLICATIONS
Maximum activity per
Nuclide Application Typical activity source decayed
30 years
Am-241/Be Neutron Moisture Gauging 1.11 GBq–9.25 GBq 8.8 GBq
Co-60 Sterilisation Plants 4 PBq–400 PBq 8 PBq
Co-60 Industrial Radiography Up to 45 TBq 872 GBq
Co-60 External Beam Therapy Up to 1000 TBq 20 TBq
Cs-137 Industrial Radiography Normally up to 3.7 TBq 1.85 TBq
(sources available to
81 TBq)
Co-60 Medical Brachytherapy Up to 74 GBq 37 GBq
Ir-192 Medical Brachytherapy Up to 370 GBq Nil
Ir-192 Industrial Radiography Up to 11 TBq Nil
Se-75 Industrial Radiography 1.11 TBq Nil
Sr-90 Medical Radiography ~1 TBq ~500 GBq
The report provides guidance on the technical, administrative and economic issues associated
with SHARS from the moment they cease to be in use through to disposal, including
temporary storage, transport, conditioning and interim storage. Detailed rules and regulations
for transport are outside the scope and relevant transport documents are referenced for that
purpose.
The risks associated with handling SHARS are such that many users may not have the
capability to manage them safely. This guidance aims to provide understanding of these
processes to those organisations which may require expert services in the field or intend to
establish the required infrastructure.
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1.4. STRUCTURE
The first part of this report (Section 2) is structured in such a way as to provide an
understanding of the nature of SHARS, including source manufacture and the nature of the
equipment that uses them. Section 3 identifies some of the issues that need to be considered in
formulating a generic approach to the management of SHARS. The report then progresses
sequentially through the steps that form the waste management process for spent sealed
sources (Section 4). This begins with a general description of the sealed source management
process and is followed by descriptions of the issues that affect transport; treatment,
conditioning and interim storage; and finally, discussion of issues leading to the development
of disposal. The report contains many illustrations and photos provided by the contributors of
the draft. Only where it was specifically requested the copyrights were quoted.
There is a section that discusses the legal, regulatory and economic considerations (Section 5)
that play an important role in the establishing and implementation of sealed source
management.
The Appendix provides summary descriptions of the current high activity sealed source
management undertaken in a number of countries to demonstrate a range of scales of
operation and states of advancement.
1.5 DEFINITIONS
For the purpose of this report, the following terms are used within the following definition:
Sealed source Radioactive material that is (a) permanently sealed in a capsule or (b)
closely bounded and in a solid form. The capsule or material of a
sealed source shall be strong enough to maintain leaktightness under
the conditions of use and for which the source was designed, also
under foreseeable mishaps [3].
Device or equipment Complete equipment including sealed source, source holder plus all
other mechanical and electrical components.
Source holder Components that contain the sealed source in the shielded position
plus the shielding material within the device.
Storage (interim) The placement of SHARS containing equipment in a nuclear facility
where isolation, environmental protection and human control (e.g.
monitoring) are provided with the intent that the spent sources will be
retrieved for exemption or processing and/or disposal at a later time.
Temporary storage The placement of SHARS containing equipment in a storage facility
within the user’s premises where isolation, environmental protection
and human control (e.g. monitoring) are provided with no intention
of any treatment and with the intention that the SHARS be removed
to an SRS facility within a reasonably short period of time
(preferably not more than a few months).
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2. CURRENT STATUS OF SPENT HIGH ACTIVITY RADIOACTIVE SOURCES
2.1. MANUFACTURE OF SOURCES
Category 1 [2] sources are normally doubly encapsulated in stainless steel forming a robust
containment that satisfies the provisions of “Special Form Radioactive Material” as described
in TS-R-1 [4]. The capsules are welded by the tungsten inert gas method (TIG welding),
electron beam or laser. Although primary encapsulation by stainless steel is preferred in the
case of gamma emitting sources, other metals have been used to suppress the activation of the
primary capsule for neutron sources.
The radioactive content is usually a metal in the case of cobalt and iridium, and salt (e.g.
chloride or nitrate) in either powder or ceramic form in the case of caesium. The large volume
of ceramic sources precludes their use above approximately 400 GBq (~11 Ci) but ceramic is
the preferred option for smaller sources where the lower dispersability and insolubility of a
ceramic material are desirable features.
2.2. WORLD INVENTORY
Accurate information on the numbers of high activity sealed sources in use worldwide is not
available. Furthermore, the constantly changing status by the deployment of new sources and
decommissioning of old sources makes any attempt to obtain an accurate number of SHARS
difficult. An estimate of source numbers was made by the IAEA based on data available in
IAEA-TECDOC-620 “Nature and Magnitude of the Problem of Spent Radiation Sources” [5].
This included information on high activity sources such as commercial irradiators and
teletherapy devices. The number of irradiators for sterilisation and food preservation was 142
(average 40 PBq Co-60 or 400 PBq Cs-137). Due to the close regulatory scrutiny of such
irradiators, this is likely to have been an accurate figure. The number of teletherapy devices
was estimated as 2,600. While it may seem reasonable to assume that the high activity of such
sources would also ensure close regulatory scrutiny and therefore accurate inventory
information, there is some evidence that this figure may have been an underestimate.
Information from one major supplier1of radiation therapy equipment indicates that 2,500 units
have been installed by one company alone. The company has encapsulated over 5000 sources
and over 1500 PBq (40 million Ci) over the past five decades and installed over 2500 cobalt-
60 radiation therapy units in more than 50 countries. It is therefore concluded that a very large
number of SHARS exists.
2.3. EXAMPLES OF EQUIPMENT CONTAINING HIGH ACTIVITY RADIOACTIVE
SOURCES2
2.3.1. Industrial irradiators
Gamma irradiators are used worldwide for, inter alia, sterilization of medical supplies and
food irradiation (see Figure 1). These involve the use of arrays of very high activity sources
(average total activity per sterilisation unit is 40 PBq, over one million curie, Co-60). Large
volumes of material to be irradiated are passed through the source beam after entering the
irradiation room via a labyrinth system. A similar labyrinth with access control is provided for
1 Private communication.
2 Examples given above are from civilian applications. Management aspects provided in this report apply equally
to sources used for military applications.
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